Investigating the relationship between seismic and infrasonic source mechanisms in debris flows

Debris flows are sources of both seismic waves and infrasound, whose radiation processes and their relationship are still poorly investigated. We present the analysis of the seismic and infrasonic signals radiated by a debris-flow event in the Gadria catchment (Eastern Italian Alps). Although results confirm that seismic and infrasonic signals originate from independent and decoupled processes, they exhibit near-field correlation when the primary infrasonic source is weak, as a significant component of the recorded infrasound is produced by the transmission of the seismic waves into the air near the sensor. Moreover, results suggest that the infrasonic source mechanism within debris flows effectively develops only when flow discharge is above a certain threshold and mostly at topographic steps. We also estimate the flow velocity using only infrasound data, obtaining good match with the values derived from flow-depth data. Eventually, the comparison of the recorded seismic amplitude with flow-depth and basal-force data suggests that the seismic radiation by debris flows is affected by the variations in the sediment discharge during the event. Our results provide additional constraints on the infrasonic and seismic source mechanisms within debris flows.